This invention relates to an electrophotographic image carrier of the type which has a vapor-deposited, inorganic photoconductive layer that is bonded to an electrically conductive metal or metallized substrate by means of an intermediate layer.
At the present time, of the known inorganic photoconductors, the most suitable base material for the commercial manufacture of electrophotographic image carriers has been found to be the amorphous, vitreous selenium because of its good charge-storing and sufficient electric conducting capabilities. When amorphous selenium, or selenium doped with halogen, or selenium-containing compounds and mixtures, such as mixtures with arsenic are used as a photoconductive layer that is vapor-deposited on a substrate or a base, the problem of improving the bond of this layer - which by itself has insufficient adhesive properties - with the substrate is continuously encountered.
The different thermal expansions of the base and of the photoconductive layer may result in breaking away or flaking of the layer from its base. It is further noted that the electrophotographic image carrier is, during commercial use, occasionally jarred or, developing balls contact its surface in such a manner that tears or flakings may result.
In the commercial use of selenium as a photoconductive layer, the selenium is generally applied to a rigid base which has the shape of a cylindrical drum. For the purpose of increasing the operational speed of an electrophotographic copying apparatus, it is known to use a flexible band as the image carrier. Such an arrangement is described, for example, in U.S. Pat. No. 3,146,688. In this manner, a substantial increase of the image surface and thus an increase in the operational speed is possible.
If the photoconductive layer is provided as a coating on a flexible band which is trained about rollers, the problems of adhesion of the layer to its substrate are even more pronounced since the continuous flexing of the photoconductive layer leads frequently to ruptures and flakings, particularly when the band is driven with high speeds.
There are known processes for manufacturing electrophotographic image carriers and for improving the adhesion of a photoconductive selenium layer on a substrate with diverse combinations which have the common characteristic that the photoconductive selenium layer is bonded to the substrate by means of an intermediate layer.
A method for the manufacture of an electrophotographic image carrier plate of the above-outlined type is disclosed, for example, in German Laid-Open Application (Offenlegungsschrift) No. 1,926,056. According to the process described therein, for improving the adhesion, an essentially organic intermediate layer made of a substituted silylisobutyl ethylene diamine is applied to a clean, electrically conductive base. The intermediate layer, if it is applied in a wet coating process or as a liquid solution, has to be dried and subsequently, a selenium-containing photoconductive layer is applied to the intermediate layer.
Further, British Patent No. 1,243,384 discloses a xerographic system including an electrophotographic image carrier of the above-outlined type in which, for improving the adhesion of the photoconductive layer on an electrically conductive and also an insulating base, the photoconductive layer is bonded with the substrate by means of an intermediate layer made of graphite and, according to requirements, of the residue of a carrier liquid for the graphite. Although in this manner an advantageous adhesion can be accomplished, the dried intermediate graphite layer has a substantial surface roughness so that the usually 50 to 100-micron thick photoconductive layer applied thereto will have a surface roughness of such an extent that the image carrying surface of the photoconductive layer does not have the desired image resolution and further, this surface is difficult to clean.